Conventional hydraulically driven or hydrostatically controlled machines such as power lawn mowers include a pair of drive wheels, each of which is independently operated by a hydraulic or hydrostatic pump coupled to the mower's engine. A corresponding motor is provided for each drive wheel, each motor being powered by one of the pumps. Each pump includes a control lever for regulating fluid pressure and direction to its corresponding motor. In such a manner the drive wheels of the power device (e.g. lawn mower) are independently controlled so that each may be rotated at variable speeds in both forward and reverse directions.
Accordingly, each drive wheel of hydrostatically controlled mowers may be driven in either the forward or reverse direction and the mower may therefore be turned through various angles. Hand levers for manipulation by the operator on such mowers are typically provided on handle members for moving the individual pump control levers into desired positions. The above described power lawn mowers are commonly referred to as zero turning radius mowers because if operated in a particular or predetermined manner, the right drive wheel and left drive wheel may be rotated in opposite directions at similar speeds thereby allowing the mower to conduct approximate zero radius turns about a central axis or point located between the drive wheels. This, of course, provides for improved maneuverability in tight environments. Exemplary zero turning radius mowers are disclosed, for example, in U.S. Pat. Nos. 5,077,959; 4,967,543; 4,991,382; and 4,920,733.
Conventional power mowers are generally divided into three separate categories: (i) self-propelled walk-behind mowers; (ii) mowers operated by a seated occupant; and (iii) mowers operated by a standing occupant.
U.S. Pat. Nos. 5,077,959; 4,967,543; 4,991,382 and 4,920,733 disclose typical walk-behind power mowers including hydrostatically or hydraulically controlled rear drive wheels. Unfortunately, the operator of walk-behind mowers such as these is forced to continually walk during mowing operations, thereby leading to fatigue. This is, of course, a disadvantage associated with walk-behind mowers, especially in hilly environments. As a result of operator fatigue, mowers controlled by walking operators are generally less productive over extended periods of time. A further disadvantage of walk-behind mowers is that the operator's feet are left unprotected and thus exposed to potentially dangerous flying debris.
Turning now to power mowers operated by seated occupants, U.S. Pat. Nos. 3,483,682; 4,487,006; 4,316,356; and 4,998,948 disclose typical such mowers. Unfortunately, seated occupant operated mowers tend to have fairly high centers of gravity (i.e. they are top heavy) due to the position of the operator's center of gravity which is far from the ground. Such high centers of gravity render mowers operated by seated occupants more likely to tip or roll. Because tipping and rolling is more likely to occur as such mowers operate through turns or on hills, seated operators must be very careful in such environments and work at reduced speed. Operation at reduced speeds clearly leads to reduced productivity of the mower. Additionally, seated operators have a hard time ducking under low hanging tree limbs and the like because of the fixed position of the seat and thus the lower half of the operator's body. Furthermore, seat assemblies on such mowers necessarily increase the overall cost of the mowers.
U.S. Pat. Nos. 2,354,576; 3,485,314 and 5,004,251 disclose power devices operated by standing occupants supported on trailers or sulkies. The operators of these devices (e.g. power mowers) are supported on sulky devices or trailers removably attached to the mower. Thus, the standing operator supporting trailing platforms of these patents are not actually part of the mower, but rather are mower attachments which must be removed or folded up during mower transport. While the trailing platforms or sulky devices of U.S. Pat. No. 2,354,576 and 5,004,251 provide for mower operation by a standing occupant, they greatly extend the overall length of the mower system and are rather bulky in nature. Thus, the sulky or standing occupant platforms of these patents must be disconnected or folded up during transport of the mower. This is burdensome and inconvenient. A further problem with removable trailing platforms such as those disclosed in U.S. Pat. Nos. 5,004,251 and 2,354,576 is that they significantly extend the length of the mower thereby decreasing maneuverability in tight spaces. Additionally, because these sulky or attachment devices are not actually part of the mower, they must often be purchased separately thus increasing the overall cost of the mower system.
U.S. Pat. No. 4,878,339 discloses a power lawn mower including a selectively deployable riding platform for supporting a standing operator or occupant. The mower of U.S. Pat. No. 4,878,339 may be operated either as a walk-behind mower or alternatively as a standing occupant/operator mower depending upon whether or not the standing operator platform is deployed. In other words, because the platform is selectively deployable it is non-fixedly mounted to the mower. Unfortunately, in the walk-behind mode, this mower experiences the above-referenced problems associated with typical walk-behind mowers.
In the standing operator mode (i.e. when the riding platform is deployed), the power mower of U.S. Pat. No. 4,878,339 experiences numerous problems. Firstly, the position of the riding platform lengthens the overall length of the mower and renders it difficult to maneuver in tight areas. Furthermore, while the platform of this patent provides for a fairly low center of gravity, its location well behind the rear drive wheel axis and extension substantially behind the rear drive wheels renders it more likely to bottom out or contact the ground when the mower goes over curbs, bumps, or the like.
If the power mower of U.S. Pat. No. 4,878,339 were operated so as to conduct a substantially zero radius turn, the rear drive wheels would be operated in opposite directions at similar speeds and the central turning point would be located between the rear wheels along the rear drive wheel axis. Because the standing occupant platform of the mower of the '339 patent is not located at or near this central turning axis (i.e. the platform is located well behind the rear drive wheel axis in the standing operator mode), the operator is adversely affected by centrifugal force created during approximate zero radius turns of the mower. The standing operator is also more affected by centrifugal force created during other mower turns. Due to this centrifugal force, the standing operator or occupant of the mower of the '339 patent is forced to take turns at slower speeds thus reducing the overall productivity of the mower over extended periods of time.
Another problem with the position of the platform of the U.S. Pat. No. 4,878,339 mower is that its location creates a greater tendency for the mower to "pop wheelies" upon acceleration, especially going up hills, because the mower's center of gravity is moved rearward when it is operated by a standing occupant. The position of the platform of this patent often necessitates the standing operator leaning forward prior to and during acceleration in order to avoid popping such wheelies and possibly tipping over the mower.
It is apparent from the above, that there exists a need in the art for a power lawn mower operable by a standing occupant including a platform for supporting the standing occupant, the platform being positioned on the mower so as to result in the following advantages: (i) a low mower center of gravity resulting in improved drive wheel traction and less susceptibility to tipping or rolling; (ii) a lessened overall length of the mower so as to render it highly maneuverable in tight spaces and environments; (iii) a reduced tendency of the standing operator platform to bottom out or contact the ground when the mower goes over curbs, bumps, or the like; (iv) a platform positioned in a zero turning radius mower such that the operator is substantially unaffected by centrifugal force created during approximate zero radius turns, thereby allowing the operator/mower to take such turns at higher speeds; (v) a platform positioned in a manner such that the mower is less likely to pop wheelies upon acceleration; etc. Each of the above advantages is accomplished by positioning the standing operator platform of the mower substantially between the rear drive wheels.
It is the purpose of this invention to fulfill the above-described needs in the art, as well as other needs which will become apparent to the skilled artisan from the following detailed description of this invention.